The current wave of 3-dimensional (3D) movies is gaining popularity and made possible by the ease of use of 3D digital cinema projection systems. However, the rate of rollout of those systems is not adequate to keep up with demand, and is further a very expensive approach to obtaining 3D. Earlier 3D film-based systems were besieged by difficulties, including mis-configuration, low brightness, and discoloration of the picture, but are considerably less expensive than the digital cinema approach. In the 1980's, a wave of 3D films were shown in the US and elsewhere, making use of a lens and filter designed and patented by Chris Condon (U.S. Pat. No. 4,464,028). Other improvements to Condon were proposed, such as by Lipton in U.S. Pat. No. 5,481,321. Subject matter in both references are herein incorporated by reference in their entirety.
One lens configuration, the “over and under” lenses or “dual-lens” arrangement (e.g., an upper lens for projecting an image for one eye, and a lower lens for projecting an image for the other eye) project the corresponding left- and right-eye images with a differential keystone distortion. This arises because the upper lens (typically corresponding to the right-eye image, for example), is higher above the bottom of the screen than is the lower lens (e.g., corresponding to the left-eye image), and thus, has a greater distance to the bottom of the screen, resulting in the right-eye image undergoing greater magnification there than the left-eye image. Similarly, the left-eye image (through the lower lens) undergoes greater magnification at the top of the screen than does the right-eye image. These different magnifications can result in detrimental effects such as different depth perceptions at different portions of the projection screen, or mis-alignments between left- and right-eye images causing fatigue for the viewers.
Since this dual-lens configuration is used in many film-based and some digital projection systems, the presence of distortions such as keystoning can adversely affect many 3D film or digital presentations. In general, projection systems that have non-identical projection geometries for the respective left- and right-eye images are susceptible to this distortion (e.g., digital projection systems using time-domain multiplexing of the imagers to project left- and right-eye images from the same physical imagers with identical geometries do not suffer from keystone distortions).
While distortion compensation can benefit both film-based and digital presentations, for film-based systems, it is further desirable to improve the 3D presentation quality by improving the image separation, color, and brightness so as to compete with digital cinema presentations.
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